The invention concerns a method for blow molding containers, in which preforms made of a thermoplastic material are heated in a heating line and then transferred to a blowing system, in which the preforms are shaped into containers by the action of blowing pressure inside blow molds, which consist of at least two blow mold segments, and in which method the preforms are conveyed together with the blow molds along at least part of a peripheral path of a rotating blowing wheel.
The invention also concerns a device for blow molding containers, which has a heating line for heating preforms made of a thermoplastic material and is provided with a blowing system, which has at least one blowing station arranged on a blowing wheel for shaping the preforms into containers, and in which the blowing station is provided with mold supports for supporting each blow mold segment.
In container molding of this type by the action of blowing pressure, preforms made of a thermoplastic material, for example, preforms made of PET (polyethylene terephthalate), are fed to different treatment stations within a blow-molding machine. A blow-molding machine of this type typically has a heating system and a blowing system, in which the preform, which has first been brought to a desired temperature, is expanded into a container by biaxial orientation. The expansion is effected by means of compressed air, which is fed into the preform to be expanded. DE-OS 43 40 291 explains the process-engineering sequence in this type of preform expansion.
The basic design of a blowing station for container molding is described in DE-OS 42 12 583. Possible means of bringing the preform to the desired temperature are explained in DE-OS 23 52 926.
Various handling devices can be used to convey the preforms and the blow-molded containers within the blow-molding device. The use of transport mandrels, onto which the preforms are slipped, has proven especially effective. However, the preforms can also be handled with other supporting devices. Other available designs include the use of gripping tongs for handling the preforms and the use of expanding mandrels, which can be inserted in the mouth section of the preform to support the preform.
The above-explained handling of the preforms occurs, for one thing, in so-called two-step processes, in which the preforms are first produced by injection molding and temporarily stored and then later conditioned with respect to their temperature and blown into containers. For another, the preforms can be handled in so-called one-step processes, in which the preforms are first produced by injection molding and allowed to solidify sufficiently, then immediately suitably conditioned with respect to their temperature, and then blow molded.
With respect to the blowing stations that are used, various embodiments are known. In the case of blowing stations that are arranged on rotating transport wheels, book-like opening of the mold supports is often encountered. However, it is also possible to use mold supports that can be moved relative to each other or that are guided in a different way. In stationary blowing stations, which are suitable especially for accommodating several cavities for container molding, plates arranged parallel to one another are typically used as mold supports.
As a result of steadily increasing demands on the productivity of blow-molding machines, blowing wheels are used which rotate relatively fast and have a relatively large number of blowing stations. The large number of blowing stations results in blowing wheels with large diameters, and the high speeds of rotation result in large braking and accelerating forces due to the high kinetic energy of the moving masses.
To diminish these negative effects, it has already been proposed that the blowing wheels be designed with a compact arrangement of blowing stations. DE-OS 199 48 474 describes a large number of design variations. However, so far no design has been found that allows improved compactness of the blowing wheel and at the same time allows a simple basic mechanical design.
DE-OS 103 46 089.6 describes the arrangement of blowing stations on a rotating blowing wheel, in which a parting plane of the blow mold segments is oriented obliquely backward opposite the direction of movement of the blowing wheel. To carry out feeding and delivery operations, the two blow mold segments are swung open to allow access to the inside of the blowing station.